Ok, help us out: Given that we have Wrk set to max out at 256 concurrent requests, what would the ideal tuning for php-fpm? A pull request would be ideal, but you can also just tell us. :)
What happens now is 256 workers running and 256 simultaneous requests occur. So php-fpm sees 256 workers busy, 0 idle. The minimum idle is 256, so it attempts to start 256 additional processes.